Earthquake strikes off southern Philippines

Just before 4:30 a.m. local time, a M=6.8 earthquake shook the southern Philippines. According to the USGS, the earthquake occurred at a depth of 26 km, and was widely felt.

Just before 4:30 a.m. local time on 29 April, a M=6.8 earthquake shook the southern Philippines. According to data from the USGS, the quake occurred offshore at a depth of 26 km, and was a nearly pure thrust event. Fortunately, despite the magnitude of the earthquake, the USGS estimates that economic losses will remain very low, and there are unlikely to be any fatalities. This is likely because the region exposed to the strongest shaking is sparsely populated. However, reports are still coming in.

This Temblor map shows active faults in the Philippines (From: G-EVER), as well as the location of today’s M=6.8 earthquake. While there is a large subduction zone to the east, the depth at which today’s earthquake occurred (26 km) suggests it occurred in the upper crust. Additionally, the strike of the fault on which today’s earthquake took place is roughly parallel to those mapped onshore.

Based on the Global Earthquake Activity Rate (GEAR) model, which is available in Temblor, this earthquake should not be considered surprising. The GEAR model uses global strain rates and seismicity since 1977 to forecast the likely earthquake magnitude in your lifetime (1% chance per year) anywhere on earth. To view the model, click here. From the figure below, one can see that the area in which today’s earthquake occurred is susceptible to M=7.0 earthquakes.

This Temblor map shows the location of today’s M=6.8 earthquake in the Philippines. It also shows the Global Earthquake Activity Rate (GEAR) model, which forecasts the likely earthquake magnitude in your lifetime anywhere on earth. Based on global strain rates and seismicity since 1977, today’s earthquake should not be considered surprising as the region is susceptible to M=7.0 earthquakes.

By looking at the historical earthquake database on the USGS website, we can also say that this region has experienced large earthquake in the past. In fact, in the last 90 years, there have been 4 other M=6.6+ earthquakes. The largest of these was a M=7.5 in 1984. However, this quake occurred at a depth of over 200 km, much greater than today’s (26 km), and likely did not result in much disruption. Should any new reports come in about damage or fatalities in this most recent quake, we will update this post.